The invention is directed to polyols based on a first initiator having a relatively high functionality, averaging greater than eight, and optionally a second initiator, having low functionality, i.e. a two to eight nominal functionality initiator molecule. Another aspect of the invention is a process for making the polyols. The invention is also directed to a process for producing polyurethane foam by reacting a polyol of the invention with isocyanates, and the foam produced thereby.
The production of polyurethane foams by reacting polyisocyanates with isocyanate-reactive compounds, for example polyether polyols, hereinafter also referred to generally as polyetherols, and, if desired, chain extenders and/or crosslinkers in the presence of catalysts, blowing agents and, if desired, flame retardants, auxiliaries and/or additives is generally known. See U.S. Pat. Nos. 4,554,295; 4,810,729; 5,143,941; 5,260,347; 5,290,823; 5,830926; and 6,228,899; the disclosures of which are incorporated herein by reference.
Characteristics of polyurethane foams, such as flexibility, rigidity, density, hardness, strength and elongation properties, can be adjusted by altering the starting materials, reactant ratios and other reaction parameters. Altering the polyether polyols used to form polyurethane foam is a well-known means of changing foam characteristics. The choice of initiators, and in particular the functionality of initiators, is known to affect the resulting polyol and, consequently, the characteristics of the foams made therefrom.
Conventionally, rigid polyurethane foams are made from polyols having a nominal functionality of two to eight. It is desirable to make rigid polyurethane foams from isocyanate-reactive compounds having functionality greater than eight to achieve improved properties such as rigidity, density and dimensional stability. However, previous attempts to make polyols of functionality greater than eight have encountered difficulties rendering their industrial manufacture impractical. In particular, initiators of functionality greater than eight are often difficult-to-process solids and may be prohibitively expensive for use on an industrial scale for making polyols. Polyols based on higher functionality initiators also disadvantageously tend to have high viscosity and/or poor filterability. Thus, there is a need for polyols for use in rigid polyurethane foam formation, having a functionality of greater than eight, which are inexpensive and have improved processability.
Flexible polyurethane foams are conventionally made using triol-based polyols having a nominal functionality of three. Flexible foams made from such polyols have adequate hardness, tensile, tear, elongation and compression set performance. A drawback of the triol-based polyols is their generally low reactivity (rate of molecular weight build) relative to current state of the art polyols, such as glycerin/sorbitol co-initiated polyols. The low reactivity results in longer cycle times in making foam, which increases the cost of foam manufacture. It is recognized in the art that higher functionality polyols build molecular weight faster in the polyurethane foam during the reaction, thus effectively providing higher reactivity. To utilize the faster molecular weight building feature of higher functionality polyols, sorbitol- and sucrose-based polyols have been used in conjunction with glycerin-based polyols to form flexible foam. The polyol components resulting from use of the two initiators have a higher reactivity than triol-based polyols and provide greater foam stability.
A drawback of the glycerin/sucrose- and glycerin/sorbitol-based foams is that, while foam hardness is about the same as that of a triol-based foam, the tensile, tear and elongation properties are reduced in foams based upon sucrose or sorbitol polyols. This loss of tensile, tear and elongation properties causes difficulty in fabricating finished articles. Reduction of tensile, tear and elongation also results in reduced performance, particularly durability performance. Thus, there is a need for new polyols, for use in flexible polyurethane foam formation, which provide higher reactivity than a triol-initiated polyol, but which provide the same as or better tensile, tear and elongation properties to the foam.
Attempts have been made to use starch hydrolysates as the initiator for polyols. Starch polymer has been described in the literature many times and is composed of chains of glucose rings linked together by ether bonds. In hydrolyzed starch, the glucose rings comprising the starch polymer molecule remain intact while the polymer is broken into smaller oligomers at the ether bond between glucose rings. Starch hydrolysate can be alkoxylated to form a polyol, but tends to undergo undesirable side reactions during the alkoxylation process. The side reactions are believed to be due to the presence of hemiacetal glucose rings as end units in the oligomers resulting from hydrolysis of the starch polymer. These hemiacetal end units are in equilibrium with the hydroxyaldehyde form of glucose. In the presence of strong base, the hydroxyaldehyde/hemiacetal form of glucose is less stable than the acetal linkages and tends to undergo undesirable side reactions. Typically, in the presence of a strong base, such as the alkali metal or alkaline earth metal oxide bases generally used in catalyzing the alkoxylation reaction to make polyetherols, the hemiacetal ring converts to the hydroxyaldehyde, which then undergoes various side reactions including aldol condensation and Cannizzaro reactions to form by-products. These by-products can cause color changes and other undesirable characteristics in the polyol. Use of hydrolysated starch, unhydrogenated, as an initiator tends to result in polyetherols that are unacceptable for modem polyurethane foam production due to the presence of by-products that are difficult and expensive to remove from the polyol. Thus, there is a need for polyols of functionality greater than eight that are made from inexpensive raw materials and processes without the inclusion of by-products.
It is an object of the invention to provide polyols which overcome the above-described drawbacks of the prior art and to provide polyols, polyol components and polyurethane foam based upon one or more initiators having a molar average functionality of greater than eight.
The present invention provides a polyether polyol comprising the reaction product of at least one alkylene oxide and at least one first initiator comprising a plurality of species having alkylene oxide reactive hydrogens, wherein the first initiator has a molar average functionality of greater than eight and the plurality comprises in most major part species having a functionality of less than eighteen, and optionally, at least one second initiator having alkylene oxide reactive hydrogens and a nominal functionality of 2 to 8. For purposes of this invention, the term most major part is understood to mean more than 50% and, preferably less than 100%. The plurality may comprise species having a functionality of less than eighteen in an amount greater than 60%, and desirably the amount ranges between 65 and 95%. In one embodiment, the first initiator comprises a hydrogenated starch hydrolysate, which may comprise species each having a nominal functionality of from 6 to about 27, wherein between 80 and 90% of the species have a functionality of less than eighteen.
The invention also provides a polyether polyol comprising the reaction product of at least one alkylene oxide and at least one first initiator having alkylene oxide reactive hydrogens, being substantially free of hydroxyaldehyde functional groups, and having a molar average functionality in the range of greater than eight to less than eighteen, and optionally, at least one second initiator having alkylene oxide reactive hydrogens and a nominal functionality of 2 to 8. In one embodiment, the first initiator comprises a plurality of species. This plurality of species may comprise species each of which has a nominal functionality of six or greater.
Polyols of the invention may comprise about 5 to about 100 wt % of alkoxylated species each having a nominal functionality greater than 8.
In one embodiment, the second initiator has a nominal functionality of 2 to 3. This embodiment also provides polyether polyols wherein about 5 to about 50 wt % of the polyol comprises alkoxylated species each having nominal functionality greater than 8.
The invention further provides a process for making a polyether polyol comprising the steps of providing at least one alkylene oxide and providing an initiator component comprising at least one first initiator having alkylene oxide reactive hydrogens, being substantially free of hydroxyaldehyde functional groups and having a molar average functionality in the range of greater than eight to less than eighteen; and optionally, at least one second initiator having alkylene oxide reactive hydrogens and a nominal functionality of 2 to 8; and reacting the at least one alkylene oxide with the initiator component to form a polyether polyol. Optionally, step c) may be conducted in the presence of a catalyst. In one embodiment, the first initiator comprises a plurality of species each having nominal functionality of six or greater. In another aspect of the invention, the first initiator comprises a hydrogenated starch hydrolysate. In yet another aspect of the invention, the initiators may be blended to form the initiator component before reacting the at least one alkylene oxide with the initiator component.
In a preferred embodiment, a polyether polyol is provided comprising the reaction product of at least one alkylene oxide and at least one first initiator, having alkylene oxide reactive hydrogens, comprising a hydrogenated starch hydrolysate having a molar average functionality of greater than eight, and optionally, at least one second initiator having alkylene oxide reactive hydrogens and a nominal functionality of 2 to 8. In a yet further embodiment, the second initiator comprises species having a nominal functionality of 2 to 3 and the ratio of the first and second initiators is selected such that the polyether polyol has a molar average functionality from about 2.2 to about 4.
The process may include co-initiation of the polyol or polyols may be initiated separately and used alone or in combination.
The invention further provides processes and polyols wherein the first initiator comprises a plurality of species having nominal functionality of six or greater. It is another object of the invention to provide a process wherein about 5 to 100 wt %, preferably 10 to 100%, most preferably 20 to 100%, of the polyol comprises alkoxylated species of nominal functionality greater than 8. The upper limit of 100% can advantageously be lowered as necessary to improve processability.
The invention also provides process for making polyols for flexible foam including use of at least one second initiator having a nominal functionality of 2 to 3. It is a further object of the invention to provide a process wherein about 5 to 50%, optionally 7 to 40% and preferably 10 to 30 wt % of the polyol are alkoxylated species of nominal functionality greater than 8.
In a preferred embodiment, the first initiator comprises a hydrogenated starch hydrolysate (HSH) and/or the second initiator comprises glycerin and/or diethylene glycol (DEG).
It is also an object of the invention to provide polyether polyols and polyurethane foams that are the reaction products of the above-described processes.